The present invention relates to apparatus for detecting fluid flow, as in apparatus for detecting or measuring the rate or the volume of flowing fluid. In particular, this invention relates to so-called "bearingless" or orbital-ball flow detection apparatus.
Generally there are two types of flow detectors that utilize a fluiddriven orbital ball. In one type, which may conveniently be called the "axial-flow" type, the fluid flows along a generally cylindrical passage. Vanes in the passage develop a lengthwise spiraling flow pattern. The orbital ball is constrained to travel along a circular race or track around the axis of the passage. The spiralling flow pattern causes the ball to orbit past the ball sensor. In another type, which may conveniently be called the "toroidal" type, a ball moves along the toroidal flow passage past a sensor. The fluid enters the toroidal passage tangentially and the fluid leaves the toroidal passage along a tangential path or along an axial exit port. U.S. Pat. No. 3,861,210 issued Jan. 21, 1975 to T. L. B. Griverus discloses both axial-flow and toroidal types of orbital ball flow detectors.
Magnetic and other forms of ball sensors have been used in orbital ball flow detectors. Photoelectric ball sensors are known in toroidal-type flow detectors, as in U.S. Pat. No. 3,861,210, supra. With photoelectric ball sensing, the ball need not have critical physical properties required by other sensors. Accordingly, there is greater freedom of choice of material for the ball. For example, the density of the ball can closely approximate the density of the liquid flowing in the flow detector, for extending the linearity of flow rate versus orbital frequency over a wider range of flow rates. Heretofore, the use of photoelectric ball sensors in orbital ball flow detectors has apparently been limited to the toroidal type of flow detector.